Jon,
Just a little extra to your comment in post number 6 above re; a possible Welsh connection. In "Coal Trade Wagons," also by Len Tavender, on page 27 there is a drawing of another Gloucester built wagon from 1884. It is of 'Locket's Steam Coal Compy' of Merthyr No 362, load 10 tons with a rolled iron underframe and self contained buffers. Body size 14' 11" over headstocks and 7' 3" wide. At the door end there is a large letter M in the style of the Midland Railway's 'M' over the bottom four planks. At the closed end of the wagon is a large 'L' covering the lowest four planks, next to which is script on the second plank in two lines - "Empty to Mardy Colliery," under which is written "Taff Vale Raily." The bottom plank has the script
"Tare 4-19-0." Body colour according to Tavender's notes is likely black with white unshaded lettering. Wheelbase is 8' 3" length overall is 17"6."
Probably too much information, but it is sometimes of interest to have some more background information when building stock.
Best wishes
Rich